<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>面试题2</title>
</head>
<body>
    
<script type="text/javascript">
    function fun(n,o){
        console.log(o)
        return{
            fun:function(m){
                return fun(m,n)
            }
        }
    }
    var a = fun(0) // undefined // a= {fun:function(m){return fun(m,0)}}
    a.fun(1) // 0
    a.fun(2) // 0
    a.fun(3) // 0

    var b = fun(0).fun(1).fun(2).fun(3) // undefined ,0,1,2
    var c = fun(0).fun(1) // undefined ,0
    c.fun(2) // 1
    c.fun(3) // 1
</script>
</body>
</html>